Between planets that orbit so close to their stars that their year is measured in hours to the recently discovered planet around the closest star to Earth (Proxima Centauri b), exoplanets have never been closer. We will discuss what it would be like to visit an ultra-short-period planet, as well as a not-entirely-crazy plan to send probes to Proxima Centauri b.

The lecture will be held on Boise State’s campus in the Multi-Purpose Classroom Building, room 101 at 7:30p. Weather permitting, we will then star-gaze on top of the Brady Garage at 8:30p until 11p.

The last day of the meeting is always to hardest to write about because I’m usually so busy wrapping things up, I don’t have time to write (hence my writing this post from Boise on the Sunday AFTER the conference).

In any case, lots of talks and goodbyes on the last day, but one talk that stands out for me came from Andrew Hesselbeck Hesselbrock, one of David Minton‘s grad students at Purdue’s EAPS. The talk tackled one of the longest-standing mysteries in solar system science: Why hasn’t Phobos crashed into Mars yet?

Phobos and Deimos have probably been orbiting Mars for about the age of the solar system, 4.6 billion year. So if this orbital decay were the whole story, it would be mean we just caught Phobos right at the end of its life, about as likely as catching someone driving from Boise to New York City right as they pass through the Holland Tunnel*. Hesselbeck Hesselbrock suggested in this talk that we’re actually seeing a recurring phase in a much more dramatic story for Phobos.

Instead of steadily spiraling in toward Mars for 4.6 billion years, Phobos (or at least a proto-Phobos) already spiraled in toward Mars before, millions of years ago. But when the satellite got close enough to Mars, Mars’ gravity ripped it apart and formed a disk of rubble around the planet. Soon after forming, this disk spread out, some moving toward Mars (and ultimately impacting the surface) and some moving away. Eventually, the bits that moved outward moved far enough away from Mars that they re-coalesced. In fact, Hesselbeck Hesselbrock speculated that Phobos has actually been reincarnated many times in this way, every time a little smaller than before, until we were left with the bitty moon we see today.

As crazy as this hypothesis sounds, it could answer several puzzles of the Martian system, including accounting for cyclic sediment deposits on Mars’ surface — the deposits form every time Phobos falls aparts and bits rain down on Mars’ surface.

The distance from Boise to New York City is about 2,475 miles, and the Holland Tunnel is about 9,000 feet long. Assuming a uniform driving speed, the probability of catching our driver in the tunnel is roughly equal to 9,000 feet/2,475 miles ~ 0.1%. The probability of catching Phobos during a 10 million year window over the age of the solar system is about 0.2%. Of course, you’re a little more likely to catch our driver in the Holland Tunnel, given NYC’s traffic.

Fourth day of the DPS meeting, and I found myself sitting through some great plenary talks.

First up was Kleomenis Tsiganis‘s Farinella Prize lecture “Flavors of Chaos”, a rapid-fire tour of the intricate and complex web of gravitational interactions among planets and asteroids in our solar system.

Tsiganis’s described how, using a combination of computational and pencil-and-paper techniques, we can pick at the threads in this cosmic network to tease out the early history and evolution of our solar system.

For instance, the orbits of asteroids in the asteroid belt provide subtle clues that, billions of years ago, Jupiter moved inward almost to the orbit of Mars before backing out near to its current orbit, a celestial maneuver referred to as “The Grand Tack“.

This presentation was followed by Leigh Fletcher‘s Urey Prize talk about the menagerie of seasonal changes we observe in the atmospheres for all the outer planets, from Jupiter to Neptune.

The talk was full of beautiful images of the roiling and boiling of planetary atmospheres and concluded with Fletcher’s plea to send another mission to the Uranus or Neptune before he’s too old to participate (some plans from NASA have a mission launching to Uranus or Neptune sometime in the late 2020s/mid-2030s).

Finally, we had a tag-team talk from Ashwin Vasaveda and Sanjeev Gupta about new results from Mars Curiosity rover. In addition to the stupefying images, the thing that impressed me most about the talk was just the level of detail to which we can infer the geological history of Gale Crater, where Curiosity landed.

Gupta described how the tilt of beds of sedimentary rock could be used to infer the presence of a river delta spilling out into the crater, which suggests the existence of a long-lived (millions of years) lake in the crater, probably billions of years ago when Mars was warmer and wetter.

As astronomers have discovered more potential planetary systems, it’s becoming more time-consuming to decide whether what we see are actually planets or some other thing that has fooled us into thinking they’re planets.

When astronomers find what they think might be a planetary system, one of the first things they check is whether the putative planetary system is actually stable — that is, whether the gravitational tugs among the putative planets would cause the objects to crash into one another or be thrown out of the system.

Since most of the planetary systems we find are probably billions of years, astronomers expect that real planetary systems are stable for billions of years, so if the system we’re looking out turns out to be unstable on short timescales (less than billions of years), we usually decide that it’s not really a planetary system (or that we mis-estimated the planetary parameters).

Unfortunately, doing this check usually requires running big, complicated computer codes, called N-body simulations (“N” for the number of planets or bodies in the system) for hundreds or thousands of computer-hours. That can be a problem if you’ve got planetary candidates flooding in, as with the Kepler or upcoming TESS missions.

Tamayo wanted to try a different approach: what if the same machine-learning techniques that allow Google or Facebook to decide whether someone is likely to buy an iPhone could be used to more quickly decide whether a putative planetary system was stable

So Tamayo created many, many synthetic planetary systems, some stable, some not, and had his machine-learning algorithm sort through them. According to Tamayo, his scheme was able to pick up on subtle features that helped distinguish stable systems from unstable ones with very high accuracy in a fraction of the time it would take to run an N-body simulation.

I also attended an eye-opening talk from Patricia Knezek of NSF about unconscious biases and their effects in astronomy and planetary science. Knezek explained that several studies have shown how these biases cause everyone to draw unconscious conclusions about someone based on very cursory information, such as their first name, race, gender, etc.

For instance, one study showed that the same application for a faculty position did much better if the applicant’s first name was “Brian” instead of “Karen”, even when women were evaluating the application.

Second day of DPS, and I enjoyed several fascinating sessions on exoplanet atmospheres. One of the most visually appealing talks was given by Vivian Parmentier, a planetary scientist at the Lunar and Planetary Lab.

Parmentier talked about clouds in the atmospheres of hot Jupiters, gas giant planets similar in composition and structure to Jupiter but much closer to their host stars than Mercury is to our Sun. Because they’re so close to their stars, hot Jupiters are … well … very hot, with temperatures reaching thousands of degrees.

These very high temperatures probably mean that the atmospheres contain clouds made of some exotic condensables, such as iron, cromium, or even ruby.

In his talk, Parmentier explained that understanding what kinds of clouds might form in these atmospheres is important for interpreting the growing collection of spectra collected using the Hubble and Spitzer Space Telescopes. He also showed a beautiful photo album, realistically depicting the appearances of hot Jupiters for a range of atmospheric conditions.

A detailed, if nuanced, story is emerging from these data, suggesting hot Jupiters have highly dynamic meteorology with chemically complex clouds.

I attended the Women in Planetary Science Discussion Hour, at which we addressed several issues confronting the planetary science community when it comes to expanding diversity in the field. Several planetary scientists have conducted recent studies revealing the current state of the field (e.g., the fraction of women involved in space missions has not kept pace with the fraction of women in planetary science overall).

These studies have also pointed out ways to expand our pool of talented scientists, including ways to improve faculty searches to make sure the people standing at the front of the classroom resemble more closely the people sitting behind the desks. The Women in Planetary Science blog gives a lot of relevant resources.

Kepler discovers planets using the transit technique (i.e., by looking for a planet’s shadow as the planet passes in front of its star), and so we expect only to find a small fraction of planets in our galaxy this way since it’s unlikely for a planet’s orbit to be aligned just right for a transit.

In fact, Kepler found lots of systems in which several planets transit. By looking at these systems, we can estimate how many systems should have just one planet that we can see transiting. When we do, it turns out that Kepler discovered lots more such single planets that we would expect.

This result has led some astronomers to suggest that these singly-transiting systems might have formed in a different (“dichotomous”) way from the multi-transiting systems. Instead, Spaulding suggested that culprit behind this planetary mystery was the host star.

In his talk, Spaulding pointed out that, during their youths, these stars spun fast enough that they bulged out at their equators. These equatorial bulges tugged gravitationally on their planets, causing the orbits of planets closest to the stars to re-align and leaving the orbits of planets farther away alone.

The closest planets just happen to transit, but, because the orbits of their sibling planets are aligned differently, we just can’t see them via transit. Like a lot of exoplanet research, Spaulding’s work shows that planetary systems, especially in their youth, can be dynamic, even violent, places for planets to grow up in, far from the clockwork universe Newton envisioned.

Quilling moon by Jen Grier (@grierja).

In addition to science talks, the DPS meeting has begun hosting an astronomy art show. The same folks who collect planetary spectra and analyze photometric light curves also make some beautiful art, and one of the neatest works on display was a quilling (rolled paper art) image of the lunar surface.

Before the meeting officially starts on Monday, I helped organize the DPS Educators’ Workshop, a DPS tradition where planetary science-types work with local school teachers to explain the most recent science and help them develop lesson plans and activities for their students.

We spent several hours with teachers from all over SoCal and discussed lots of great activities, but one of the most popular and visually appealing is the Art and Astronomy activity.

For this activity, we invite the teachers to recreate space-based images of planetary surfaces using pastels. As usual with this activity, the teachers at first demured but ended up creating stunning and vibrant images of craters, geysers, and river deltas.

The weather was up and down all day yesterday, but by the evening, the scattered clouds had completely disappeared, giving us a warm, clear to talk about the OSIRIS-REx mission and do some star-gazing.

The evening started off with a brilliant presentation from Alessondra Springmann, LPL grad student and scientist on the mission. I’ve included a youtube video of her presentation below.

After the talk, we looked at the Moon, Mars, and Saturn through the Physics Dept.‘s telescopes.

Thanks especially to our student volunteers. This wonderful event would not have been possible without their help.